A lot of text editors (way back to the days of Borland’s
SideKick–wow, what a blast!) provided an easy way to insert the
current date and time in the file you are editing. This is
particularly useful for a notes/journal type of thing.

Emacs (the One True Text Editor) does not provide an “out of the
box” way to do this, but a very simple piece of elisp can do it.

I put this (adapted from a suggestion found on the help-gnu-emacs
list) in my .emacs:

which allows me to press C-c d at any time to get the current date and
time in my buffer (formatted the way I like). The second function puts
it in a little block, good for seperating entries in a notes log.